ASSEMBLY OF AN ADULT TYPE ACETYLCHOLINE-RECEPTOR IN A MOUSE-CELL LINE TRANSFECTED WITH RAT MUSCLE EPSILON-SUBUNIT DNA

The mouse muscle cell line BC3H-1 expresses an acetylcholine receptor (AChR) composed of α-,β-, and δ-subunits [1]. The functional characteristics of this AChR are comparable to the non-synaptic AChR subtype in mouse muscle [2,3]. To investigate the role of the ε{lunate}-subunit, which is believed to replace the γ-subunit in forming the adult AChR subtype [4], BC3H-1 cells were stably transfected with cDNA encoding the rat muscle AChR ε{lunate}-subunit. Expression of this cDNA was under the control of a heat shock promoter, and the plasmid carried the neomycin resistance gene for selection. Several clones were isolated that had integrated the plasmid DNA in a stable form and produced ε{lunate}-subunit specific RNA after heat induction. Single-channel current recording from cells which contained abundant ε{lunate}-subunit mRNA identified a novel AChR channel having a larger conductance than the native AChR in these cells. These results suggest that the rat muscle ε{lunate}-subunit may assemble with mouse muscle α-, β- and δ-subunits to form a mouse-rat hybrid AChR with properties similar to that of end-plate channels in the mature mammalian neuromuscular synapse. The novel AChR channel appears in the surface membrane within a few hours following the rise in ε{lunate}-subunit mRNA. Thus, the notion that replacement of the γ-subunit by the ε{lunate}-subunit during development is the result of the postnatal rise in the level of ε{lunate}-subunit specific mRNA is further supported. © 1990.